Means for equalizing transmission over lines of different electrical characteristics



June 19, 1923.

, G. K. THOMPSON MEANS FOR EQUALIZING TRANSMISSION OVER LINES OF DIFFERENT ELECTRICAL CHARACTERISTICS Filed 00?.- 29 1918- 2 Sheets-Sheet 1 IN V E N TOR. .Tho

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ATTORNEY BRENT ELECTRICAL.

June 19,- 1923.

G. K. THOMPSON MEANS FOR EQUALIZING TRANSMISSION OVER LINES OF DIFF CHARACTERISTICS Filed Oct. 29 1918 2 Sheets-Sheet 2 w mwrrawwn w.

INVENTOR. a K moirgwon/ BY Z. 55

. I ATTORNEY Patented June 19, 1923.

GEORGE K. THOMPSON, OF HAPLEWOOD, NEW J', ASSIGNOR TO AMERICAN TELE- PHQNE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

MEANS EOE. EQUALIZINQ TRANSMISSION OVER LINES OF DIFFERENT ELECTRICAL CHARACTERISTICS.

Application ma October 29, 1918. Serial No. 260,158 i To all 'wfiomit may concern:

Be it known that 1, Greece K. TrroMrsoN, residing at Maplewood, in the county of Essex and State of New Jersey have in- B vented certain Improvements in Means for Equalizing Transmission Over Lines of Different Electrical Characteristics, of which the following is a specification.

This invention relates to telephone sys- 19 tems and more particularly to the provision of means whereby the transmission over telephone lines or different electrical characteristics may be equalized or rendered more uniform.

Telephone lines have, in general, different electrical characteristics varying with the length of the lines. For any particular type of line construction which may be employed the resistance, capacity, inductance and 29 leakage of the circuit increase with the length. These variations in the electrical characteristics of the different subscribers lines in a. telephone system introduce a. numbar-of variable efiects in thetelephone service rendered from difi'erent stations. i For example, the difi'erent electrical characteristics result in difierent degrees of attenuation in the alternating telephone current passing over the subscribers lines and thus give louderand more effective telephonic communication to subscribers connected by means of short lines than to subscribers connected by means of long lines. As a result, a subscriber having a long line, when connected with any other subscriber, does not receive as good telephone transmission as would a subscriber having ashort line similarly connected. Furthermore, in the common battery systems now so generally employed in all but small communities, the resistance .of the line causes a further efiect on the transmission in that it reduces the amount of direct current which the transmitter receives from the central ofilce battery and so renders it less eilicient in the genera-- tion of the alternatin telephone current.

In view of the con itions above referred to, it has not been heretofore possible to provide all subscribers with the same grade of transmission and it is one of the objects of this invention to provide means whereby this difficulty may be overcome, although other and further objects of the invention will appear from the description hereinafter given.

The objects of this invention may be se cured by associating with each line a tele-. phone transmitter whose resistance is adjusted in accordance with the electrical characteristics of the line. Where the transmis s1 on line is of high impedance, since the direct current supplied to the transmitter over the line is small, the transmitter should be of high resistance so that for a given variation of the transmitter resistance a proportionately largervariat'on of the total resistance including that of he line will be produced, and consequently a greater transmission eficiency will result. Where the line is of low impedance and the current to supplied large, the transmitter resistance should be comparatively small so that a given variation in the transmitter resistanceproduces a relatively small variation in the total resistance. Consequently the transto mission cficiency under this condition may be made little if any greater than under the first condition above mentioned.

In its more specific aspects the invention contemplates the provision of a transmitter having a resistance button whose electrodes are so arranged that by changing the position of the electrodes, as for instance by rotating them upon their axes, or by rotating the instrument itself, the resistance of the transmitter will be varied so that it may be e adjusted in accordance with the electrical characteristics of the line with which it is associated. By means of this expedient it is possible by a simple manipulation to adjust or position any transmitter of the design described to meet the requirements of any line of reasonable length so that the transmission over lines having difl'erent chzgacteristics may be substantially equalo5 ize I The inventionmay now be more fully understood from the following description when read in connection with the accom: panying drawings in which Figure 1 is a sectional view of a transmitter embodyin the principles of the invention; Figures 2, and 4 are circuit diagrams showing the electrodes of the transmitter in Figure 1 adjusted in tated so that the electrodes 7 and 8 assume the various positions in accordance with the requirements of different transmission lines; Figure 5 is a sectional view of a modified form of transmitter and Figures.6, 6, 7 8, 9, 10 and 10 are views'showing difi'erent adjustments of the electrodes of the transmitter of Figure 5.

Referring to Figure 1 a telephone transmitter is shown comprising the usual front casing 1, back casing or shell 2, mouthpiece 3, supporting bridge 4 and diaphragm 5. Suitably mounted upon the supporting bridge 4 is a carbon resistance button 6 of a well known type, comprising a back electrode 7 and av front electrode 8 between which is placed a suitable amount of granulated carbon, said front electrode 8 being so arranged as to be movable with the dia phragm 5. The front electrode 8 is similarin all respects to electrodes well known in the. art. The back electrode 7, however, is so constructed that one edge is much thinner than the other, as is clearlyindicated in Figure 1, the reasons for thisconstruction bein more fully explained hereinafter. The bac electrode is electrically connected to a binding screw 9 through the body of the resist ance button 6 which is electrically insulated from the supporting bridge 4. The front electrode 8 is connected through a spring member 10 to a binding post 11 carried by the sup rting bridge 4 and insulated therefrom. he resistance button 6 is provided with a shank l2 adaplted to be inserted in a sleeve 13 carried by t e supporting bridge 4. By rotatinglthe resistance button 6 upon the shank 12 t e granular carbon between the electrodes will be more orless compressed, depending upon the position of the electrodes. When rotated to any desired position the resistance button 6 may be locked in that position bymeans of a set screw 14. Another and more practical way would be to rotate the entire instrument upon its support and lock it firmly in place when the proper amount of rotation has been secured. -When the transmitter is to be associated 1 witha line of low impedance, the resistance button 6 or instrument itself should be rothe position shown in Figure 2 lookin down upon the electrodes from above. In this position the distance between the electrodes at the bottom where the granular carbon is collected is relatively small, and the resistance of the transmitter will accordingly" below. For a line of higher impedance such as L of Figure 3, the resistance button 6, or the instrument itself, may be iven a quarter turn so that the electrodes and 8 assume the position shown in said fi re. The resistance of the transmitter Wlll in this case have a medium value. In the case of a line such as L" of high impedance the-resistance button or instrument will be rotated another quarter turn so that the electrodes will be relatively far apart at the bottom of the button where the granular carbon is collected. The resistance of the transmitter will therefore be relatively high. It will be obvious that intermediate steps in the adjustment may also be made if desired so that a finer adjustment of the resistance of the transmitter with respect to the impedance of the line may be obtained.

A modified form of transmitteris illustrated in Figure 5 in which the same general arrangement is disclosed as in Figure 1 except that the electrodes of the resistance button 6 are of slightly diiferent character. In this case both the front and back electrode 15 and 16- are of the same thickness throughout, but each electrode is provided with a segment of non-conducting material as shown at '17 and 18 in Figure 6. The front electrode l6 is secured to and movable with the diaphragm 5 and the diaphragm 5 is electrically connected by means of a conductor 19 with the binding post 11, so that an electrical connection exists between the front electrode 16 and said binding post. The rear electrode 15 is electrically connected to the binding screw 9 in the same manner as in Figure 1. When the resistance button 6 or instrument itself is rotated to such a position that the electrodes assume the condition shown in Figures 6 and 6 the resistance of the transmitter will be at its lowest value, so that the transmitter can be used in connection with a'line of lowimpedance.

itself through an angle of about 45 degrees,

the electrodes will assume the position shown in Figure 7, so that a portion of the granular carbon is included between the in sulated segments of the electrode and the resistance of the .transmitter is increased. By a still further rotation to the position shown in Figure 8, the resistance of the transmitter will have a medium value. f Still further rotation to the position shown in Figure 9 will still further increase the resistance of the transmitter while a rotation through an angle of 180 degrees from that of Figure 6 as shown in Figures 10 and 10* will include the largest amount of carbon between the non-conducting segments, so that the resistance of the transmitter is at its highest value. 'It will be obvious that various intermediate adjustments of the resistance button may be made if a greater degree of precision is desired.

It will be seen that by means of the arrangements above .described a simple yet efficient means has been provided whereb .the telephonic transmission over lines of di ferent character may be equalized and ren deredmore uniform, so that subscribers having instruments on loops of different lengths its will receive substantially .the same trans-.

mission. It will alsobe obvious that the general principles herein disclosed may be embodied in many other organizations wide- 1 difi'erent from those illustrated without eparting from the spirit of the invention as defined in the following claims What is claimed is: n

1. A telephone transmitter for use in con nection with lines of difierent electrical characteristics, said transmitter including a resistance button having a plurality of electrodes, and at least one of said electrodes having a non-conducting segment whereby rotation of the electrodes about their axes will vary the effective conducting area of the electrodes to adjust the resistance ofthe transmitter in accordancewith the electrical which the characteristics, said transmitter includin a resistance button having a plurality of e ectrodes and saidelectrodes havin non-conducting segments whereby rotation of the electrodes about their axes will vary the effective conducting area of the electrodes to adjust the resistance of the transmitter in accordance with the electrical characteristics of the line with which the transmitter is to be used. a

In testimony whereof, I have signed my .name to this specification this 3rd day of October 1918.

- GEORGE K. THOMPSON. 

